Treatment of photographic films and plates



Patented Apr. 22', 1941 2,239,284 TREATMENT OF PHOTOGRAPHIC FILMS FritzDraisbach,

PLATES Ludwigshafen-on-the-Rhine,

Germany, assignor to Hall Laboratories, Inc., Pittsburgh, Pa., acorporation of Pennsylvania,

No Drawing. Application January 4, 1938, Se-

rial No. 183,287. In Germany December 28,

18 Claims.

This invention relates to the treatment of photographic films, platesand other bodies having sensitized coatings thereon. For purposes ofconciseness, the term films will be used herein, it being understoodthat this term is intended to cover not only films, but plates and othercarrier bodies, for example paper, for the sensitized coating which,after exposure, is developed.

This application is a continuation-in-part of my copending applicationSerial No. 55,677, filed December 21, 1935.

When photographic developers are diluted, they often form a cloudy orturbid solution. This precipitation, even when it is almost colloidal innature, has a very unfavorable effect on the developed image. I havefound that this turbidity or cloudiness in the developing solution canbe prevented by the addition to the developing solution of analkali-metal metaphosphate or tripolyphosphate, for example sodiumhexametaphosphate or sodium tripolyphosphate, either alone or incombination with alkali pyrophosphates. Instead of adding thealkali-metal metaphosphate or tripolyphosphate to the developingsolution, I may add it to the gelatine colloid which is used in coatingthe photographic films.

All developing solutions are more or less alkaline in nature. Nearly allof them are prepared by the use of certain standard alkalis, such as Isodium carbonate, borax, trisodium phosphate, and other similar alkaliswhich very readily form insoluble precipitates with the calcium andmagnesium present in hard water. These precipitates may deposit out onthe film which is It is generally considered that the function of aphotographic developer is to reduce to metallic silver or other metalthose portions of the metallic salt used as a sensitizer which have beenexposed to light, and the amount of reduction thus occurring ispresumably directly proportional to the intensity of exposure at eachindividual point. Development of a film in this manner leads to a rathergrainy image which is capable of only a moderate degree of enlargementwithout showing the granular clumps of image grain. Recent trends inphotographic research have indicated that if this so-called purelychemical method of development can be combined with a so-called physicalmethod of development in which the silver or other salt of the film isnot only reduced by the developer, but is actually flrst redissolved andthen reprecipitated out during the developing process, the resultingimage is far more fine grained than the image obtained by purelychemical development. It is believed probable that when an alkali-metalmetaphosphate or tripolyphosphate is present in the developing solution,it reacts with the silver or other salts in the emulsion, formingsoluble silver or other metal complexes which, during development, arevery slowly deposited out on the so-called activated nuclei in theemulsion. Thus, in a developing solution, the metaphosphate ortripolyphosphate probably performs two functions; first, it prevents theprecipitation of insoluble calcium and magnesium salts of the developingagent itself and of the alkalies used with the developing agent and,secondly, it probably assists in transforming a purely chemicaldeveloper into a so-called physical developer with an accompanyingimprovement in the quality of the resulting image.

Beneficial effects are obtainable by adding the metaphosphate ortripolyphosphate to the emulsion used in forming the coating of thefilm. It also seems probable that when the metaphosphate ortripolyphosphate is used in the emulsion, the improved results may bedue to reducing the concentration of certain ions such as iron, copperand aluminum by sequestering them in complex metaphosphate ortripolyphosphate compounds in which they do not have their usualdeleterious effect of decreasing the transparency of the emulsion. Thepresence of these ions in their usual form in photographic emulsion maylead to spottiness in the photograph or may decrease considerably thesensitivity of the emulsion.

The amount of metaphosphate or tripolyphosphate used is dependent uponthe purpose which it is desired to accomplish. To prevent turbidity inthe developing solution a sufficient amount of the metaphosphateortripolyphosphate to react with the calcium and magnesium in the wateris added to the developing solution. Where the sodium hexametaphosphatesometimes called "Grahams salt. The preferred alkali-metaltripolyphosphate is sodium ttripolyphosphate (NBsPaOm) Chemical andX-ray analyses show that sodium tripolyphosphate is a definite chemicalcompound which is distinct from both sodium hexametaphosphate and sodiumpyrophosphate and that it is not a mixture of the two. Sodiumtripolyphosphate is fusible and may be solidified by very rapidlycooling in a. glassy amorphous form. Under slower cooling it solidifiesin the form of crystals. The glass may be converted into crystal form byannealing. Sodium tripolyphosphate forms a crystalline hydrate of thegeneral formula NasPaomfifizO. Sodium iripolyphosphate is colorless,appearing white in the granulated crystalline form. When crushed itforms a free-flowing granular mass. By suitable precautions it may beproduced in a mass which readily disintegrates into its constituent finecrystals. Sodium tripolyphosphate is not deliquescent and particularlyin its hydrated form may be preserved indefinitely in ordinaryatmospheres without caking or picking up moisture. Sodiumtripolyphosphate is readily water-soluble in both its glassy andcrystalline forms.

The alkali-metal metaphosphates and tripolyphosphates are molecularlydehydrated phosphates" as such term is employed in Hall and JacksonPatent No. 1,903,041. For example, sodium metaphosphate (NaPO3) may beconsidered as derived from mono-sodium di-hydrogen orthophosphate by theremoval of water of constitution. Likewise, sodium tripolyphosphate maybe similarly considered as derived by molecular dehydration of a mixtureof orthophosphates which is intermediate in acidity between themono-sodium di-hydrogen orthophosphate and the di-sodium mono-hydrogenorthophosphate. phates may be regarded as salts of condensed ormolecularly dehydrated phosphoric acids which have been molecularlydehydrated to a greater extent than pyrophosphoric acid.

Although slightly more of the sodium tripolyphosphate than the sodiumhexametaphosphate is required to be added to the developing solution orto the sensitized emulsion, the sodium tripolyphosphate has theadvantage that it is more stable in the alkaline developing solutionsand therefore has less tendency than the hexametaphosphate to revert tothe orthophosphate. The crystalline tripolyphosphate may be made withoutresorting to the drastic chilling required in producing thehexametaphosphate.

The invention is not limited to the development of films containingsilver salts as the sensitizing agent, but is applicable in cases whereother sensitizers are employed such as iron salts in blue and brownprint paper, platinum salts in platino-type papers, and salts of goldused in gold-toning baths.

The metaphosphates and tripolyphos- While I prefer to use sodiummetaphosphate or sodium tripolyphosphate, the metaphosphates ortripolyphosphates of the other alkali-metals, such as potassium, lithiumand ammonium, may be employed.

Although I have described certain preferred embodiments and methods ofpracticing the invention, it is to be understood that the invention isnot limited thereto, but may be otherwise embodied or practiced withinthe scope of the following claims.

I claim:

1. A photographic film having a sensitized coating containing analkali-metal salt of a phosphoric acid which is molecularly dehydratedto a greater extent than pyrophosphoric acid.

2. A photographic film having a sensitized coating containing analkali-metal metaphosphate.

3. A photographic film having a sensitized coating containing analkali-metal tripolyphosphate.

4. The method of preventing precipitation of insoluble salts of alkalineearth metals in photographic gelatino-silver halide emulsions whichcomprises adding to the emulsion an alkali metal salt ofhexametaphosphoric acid.

5. The method of preventing precipitation of insoluble salts of alkalineearth metals in photographic gelatino-silver halide emulsions whichcomprises adding sodium hexametaphosphate to the emulsion.

6. A gelatino-silver halide photographic emulsion containing an alkalimetal salt of hexametaphosphoric acid.

7. A gelatino-silver halide photographic emulsion containing sodiumhexametaphosphate.

8. The method of preventing precipitation of insoluble salts of alkalineearth metals in photographic gelatino-silver halide emulsions, whichcomprises adding to the emulsion an alkali-metal salt of metaphosphoricacid.

9. The method of preventing precipitation of insoluble salts of alkalineearth metals in photographic gelatino-silver halide emulsions, whichcomprises adding sodium metaphosphate to the emulsion.-

10. A gelatino-silver emulsion containing an metaphosphoric acid.

' 11. A gelatino-silver halide photographic emulsion containing sodiummetaphosphate.

12. A photographic film having a gelatinosilver halide coatingcontaining an alkali-metal halide photographic alkali-metal salt of saltof a phosphoric acid which is molecularly dehydrated to a greater extentthan pyrophosphoric acid,

13. A photographic film having a gelatinosilver halide coatingcontaining an alkali-metal metaphosphate.

14. A photographic fdm having .a gelatinosilver halide coatingcontaining an alkali-metal tripolyphosphate.

15. The method of preventing precipitation of insoluble salts ofalkaline earth metals in photographic gelatino-silver halide emulsions,which comprises adding to the emulsion an alkali-metal salt of aphosphoric acid which is molecularly dehydrated to a greater extent thanpyrophosphoric acid.

16. The method of preventing precipitation of insoluble salts ofalkaline earth metals in photographic gelatino-silver halide emulsions,which comprises adding to the emulsion a sodium salt of a phosphoricacid which is molecularly dehydrated to a greater extent than pyrophos-18. A geiatino-silver halide photographic phoric acid. emulsioncontaining a sodium salt of a phos- 17. A gelatino-silver. halidephotographic phoric acid which is molecularly dehydrated to emulsioncontaining an alkali-metal salt of a a greater extent thanpyrophosphoric acid. phosphoric acid which is molecularly dehydrated 5to a greater extent than pyrophosphoric acid. FRITZ DRAISBACH.

